Generate photorealistic image from STEP files with blender
Simple in 5 steps:

1- Convert the CAD data into a format that can be imported by blender. 

2- Switch to cycles render engine. 

3- Create realistic materials, assign them to your objects and light the scene in a realistic way.

4- Render. 

5- The most important step: Forget about magic buttons that will do all of the previous 4 steps for you, this will require you to do some work and learn how to use the software.